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Vascular Plants Without Seeds (Euphyllophytes s8s3FP62cW3A_C0MqwO4HA_m…
Vascular Plants Without Seeds
All known plants, living or dead, have dibiontic life cycles
This means that they develop both a multicellular gametophyte and a multicellular sporophyte
Some organisms, like certain algae, are monobiontic
These organisms develop only a multicellular gametophyte
These organisms were the more ancient
Zygote germinates mitotically
Zygote germinates meiotically
According to the interpolation hypothesis, a zygote had a mutation that caused it to germinate meiotically instead of mitotically
This hypothesis requires one of the nonvascular clades being one of the oldest in the evolution of true plants
Hypothesis also states that the sporophyte evolves to become more and more elaborate, from the foot and seta to the apical meristem, becoming independent of the gametophyte
According to the transformation theory, the gametophyte and sporophyte both become gradually more complex, but in different species
Nonvascular plants had simple sporophytes that were dependent on gametophytes
Vascular plants had complex sporophytes and increasingly impotent gametophytes
Early Vascular Plants
Types
Rhyniophytes
Extinct
Upright stems with no leaves
Had equal dichotomous branching, which effectively meant their branches were identical in appearance and performance
Earliest definite vascular land plants
Descendants of Rhyniophytes
Zosterophyllophytes
Dead as Doorknobs
Didn't have secondary growth
Small guys
Similar to rhyniophytes, save three characteristics
Lateral Sporangia
Sporangia opened transversely
Exarch protostele xylem structure
Laid the groundwork for tree trunks
Some had outgrowths called enations that varied in length
Increased photosynthetic area
Xylem Structure
Center solid mass with no pith
Two different types of structure
Endarch Protostele
Protoxylem located in center of mass
Protoxylem differentiates early in the cellular life cycle
Metaxylem differentiates on outer edge of mass
Metaxylem differentiates later in the cellular life cycle
Exarch Protostele
Exact opposite of endarch protostele, with metaxylem in the center and protoxylem toward the edges
Siphonostele
Extra type that appeared later
Has pith in the center of xylem mass
This is similar to ferns
Lycophytes
Similar to the zosterophyllophytes, so much so that they are assumed to be descendants
Unlike zosterophyllophytes, they aren't dead as doorknobs
One main difference is the lycophytes' much larger enations that contained a lone, well-developed trace of vascular tissue
These were basically leaves, but the science term for leaves in the division lycophyta is microphyll
Another significant difference is the evolution of true roots, which allowed lycophytes to anchor firmly in the ground, absorb nutrients effectively, and grow up big and strong
Extant Species
Lycopodium
Means ground pine or club moss
Common in a variety of environments
Small Herbs
Selaginella
Less Common
So small they resemble moss
Distinguishable from lycopodiums by a flap of tissue, called the ligule, on the top of the leaves
Doesn't have an apparent use
Euphyllophytes
Origin of Euphylls
Also called Megaphylls
Both a type of leaf
One of the homoplastic structures called leaves
For the concept of homoplasy, I would think of the different breeds of dog that are collectively called pit bulls
Summarized by the telome theory
Imagine a main stem and a bunch of dichotomously branching stems. Imagine that all are aligned, and they are linked by parenchyma.
It is thought that the ancestor of leaves resembled this
With the addition of the production of sporangia, this becomes sporophyll
It is shown that leaf structures that produce sporophyll are the most successful evolutionarily
It is for this reason that megaphylls are the most common today
Similarities among Euphyllophytes
Roots with exarch xylem structure
Possession of megaphylls
They have a 30-kilobase inversion in the large single-copy region of their plastid DNA
I have next to no idea what that means
Equisetophytes
Known as horsetails
Only one extant genus
Extant species lack secondary growth and fairly small
Have a unique reproductive structure called the sporangiophore
This is where the sporangia are located in small groups
Ferns
First appeared in my period, then greatly diversified
The most familiar type of ferns, leptospporangiate ferns, make up the vast majority of monilophytes
On the underside of some fern leaves are clusters of sporangia called sori, where meiosis occurs
Vascular Cryptogams
A term used informally to refer to the plants discussed here
The reason this is considered informal is because the term groups them together by qualities they lack, which doesn't indicate close enough relation to be grouped in a clade
